The invention relates in general to ceramic composites and in particular to transparent ceramic armor.
Transparent armor is a material or system of materials designed to be optically transparent, yet protect from fragmentation or ballistic impacts. This class of materials is used in diverse applications such as, for example, protective visors for non-combat usage such as riot control or explosive ordinance disposal (EOD) actions. These materials may also be used as vehicle windows in ground, sea, and air vehicles to protect vehicle occupants or equipment (for example, sensors) from terrorist actions or other hostile conflicts. Each of these systems are designed to defeat specific threats, however, there are general requirements common to most.
Composites of ceramic and other materials such as glass and polycarbonate have been suggested as impact resistant transparent armor. For example, United States Statutory Invention Registration No. H1567 describes a transparent composite armor having a hard frangible face plate backed by a more resilient plate. United States Statutory Invention Registration No. HI519 describes the bonding of transparent aluminum oxide or magnesium oxide to a backup plate of transparent plastic. U.S. Pat. No. 7,584,689 issued on Sep. 8, 2009 to Jones et al. discloses a transparent ceramic armor with a laminate design and is incorporated by reference in its entirety herein.
As shown in FIG. 1, a known laminate 10 may include an outer strike layer 12 made of ceramic material, one or more internal layers 14 of glass, and a polycarbonate backing layer 16. Polycarbonate backing layer 16 functions as a spall catch for bullet or armor fragments. Adhesive layers 18 may be used between the other layers 12, 14, 16 to provide some crack mitigation during impact and to reduce stress from differences in the coefficients of thermal expansion.
Survivability of transparent ceramic armor, in terms of multi-hit capability, is a parameter of prime importance. However, the reflection of stress intensity waves is maximized in existing ceramic-glass “laminate” designs such as laminate 10. This is an undesirable feature and can lead to accelerated self-defeat of the transparent ceramic. A need exists for transparent ceramic armor that is better able to withstand and survive multiple hits.